As a beginner, what should be my main focus points, when practising Kata ? As you get better will these focus points change ?

As a beginner, i think that your main focus should be your stance- learning to move in front stance is not easy, let alone turning.
The techniques are only described in terms of hand movements- i.e. blocking and punching, but i think that he difficult part to master is the footwork.
Watch any Kata expert move. They never wobble. They don't make unessessary foot movements. Stance is crucial.